1. Field of the Invention
The present invention relates to a ball bearing assembly structure, an electromagnetic clutch having the ball bearing assembly structure, and a gas compressor equipped with the electromagnetic clutch.
2. Description of the Related Art
In a vane-type gas compressor used for a car air conditioner or the like, a rotary power is transmitted from an engine-crankshaft pulley to a rotor shaft 40 through a belt 60 and electromagnetic clutch 50 as shown in FIG. 1.
The electromagnetic clutch 50 has a ring-shape electromagnet 51, a prime-mover pulley 5 for passing the magnetic flux of the electromagnet 51, a plurality of rows of ball bearing 530 (see FIG. 10) for rotatably and coaxially holding the prime-mover pulley 52 to the electromagnet 51, and a follower armature plate 54 to be attracted or adsorbed to an end surface 52a of the prime-mover pulley 52 by the magnetic flux.
During engine rotation, the prime-mover pulley 52 and the ball bearing 530 holding the same are rotatively driven at all times by a belt 60.
When operating the gas compressor 1, the electromagnet 51 of the electromagnetic clutch 50 is energized to attract or adsorb the follower armature plate 54 to an end surface 52a of the prime-mover pulley 52 and join the prime-mover pulley 52 and the rotor shaft 40, thereby rotating the rotor shaft 40.
The ball bearing 530 of the electromagnetic clutch 50 conventionally has used one having an even number of balls 530a per row, e.g. fourteen as shown in FIG. 10. Generally, the ball bearing causes vibration and noise due to rotation. In the case of the ball bearing 530 rotating while undergoing a radial load due to a tension of the belt 60, vibration and noise considerably occur. Particularly when other vibration and noise levels are lowered during engine idling, the vibration and noise of the ball bearing 530 transmitted to the vehicular compartment is not negligible.
The inventor has conducted various experiments and discovered that the one factor of high vibration and noise level is an even number of balls of the ball bearing. In the ball bearing 530 having an even number of balls 530a per one row, the balls 530a are in a facing relation to have linear-symmetry arrangement between the inner race 530b and the outer race 530c. The deformation and vibration at a regular particular frequency is caused in the inner and outer races. It is to be considered that the vibration as a source also increases noise.
The present invention overcomes the foregoing problem in the conventional art and provides an electromagnetic clutch low in vibration and noise resulting from a ball bearing assembly of the present invention and a gas compressor with the electromagnetic clutch.
In order to solve the foregoing problems in the conventional art, the present invention provides an electromagnetic clutch having a ball bearing assembly having an odd number of balls per row. By providing the odd number of balls, the arrangement of balls will not be in a facing relation. The deformation in the inner and outer races during rotation of the ball bearing while undergoing a radial load is made irregular and complicated, eliminating the deformation and vibration at a regular predetermined frequency and lowering the level of vibration and noise.